Impact of speciation on the tellurium electrochemistry in choline chloride-based deep eutectic solvents

Abstract

The electrochemistry of tellurium in two different deep eutectic solvents, choline chloride - urea (ChCl-U) and choline chloride - oxalic acid (ChCl-Ox) was studied on glassy carbon (GC) and polycrystalline (Au(poly)) gold electrodes by cyclic and hydrodynamic voltammetries. Voltammetric responses associated with the redox pairs Te(IV)/Te(0) and Te(0)/Te(-II) are recorded, with a striking difference between ChCl-U and ChCl-Ox being observed in the kinetics of the Te(IV)/Te(0) couple, which is electrochemically reversible in ChCl-Ox but highly irreversible in ChCl-U. This difference is attributed to a different speciation of the Te(IV) species in the two DESs. UV–vis spectrophotometry and 125Te NMR spectroscopy demonstrate that Te(IV) exists as [TeCl6]2- in ChCl-Ox, but point to an oxo-coordinated form in ChCl-U. Accordingly, the difference in electrochemical reversibility is assigned to the lability of [TeCl6]2- contrasting with the inertness of the Te(IV) species present in ChCl-U.

Keywords

• pH of deep eutectic solvents
• Lability of tellurium complexes
• 125Te NMR
• Rotating disc electrode